Headwater lakes typically increase salmonid demographic rates at high elevations. In the thermal and trophic influences of lakes, fish grow faster, mature earlier, and have higher fecundity, than their counterparts in high elevation streams lacking lakes. We suggest that stocking fish into headwater lakes facilitates invasion of connected stream networks by several mechanisms: 1) increased demographic rates can lead to higher population growth rates, 2) larger body size potentially aids fishes in overcoming barriers to invasion of streams, and 3) headwater lake stocking confers a geographic advantage on invading fishes by allowing them access to downstream habitats that are inaccessible to fish originating at lower elevations. Impacts resulting from lake stocking may be more severe than from lower elevation stream stocking for several reasons: 1) increasingly, remaining populations of native salmonids are concentrated in fragmented, headwater refugia accessible to introduced fishes only from upstream, 2) faster population growth may increase the rate and extent of stream invasion, and 3) faster individual growth rate potentially decreases the age when predation on amphibians and fish begins.